1. Field of the Invention
The present invention relates to a method for improving EBG structures and a multi-layer board applying the same, which can form a bandgap covering a broadband frequency, so as to prevent generation of noises.
2. Description of Related Art
In a multi-layer circuit board, a power layer and a ground layer may form cavity resonators, such that in a high frequency application, noises may be generated in the power layer/ground layer and cause the power layer and the ground layer not to be equipotential surface. Namely, the noise may cause voltage variations at some positions of the power layer/ground layer. For example, when the ground layer is taken as a potential reference layer for signals or electronic devices, if the voltage variation of the potential reference layer exceeds a tolerance range, operations of the electronic devices or the circuit may be abnormal, and even an operation of the whole system may be abnormal.
Moreover, when a signal line is connected from a driver to a receiver, signals may be changed from one signal layer to another signal layer through a via. As such, the signals to be transmitted between layers may pass through the power layer and the ground layer.
If a frequency of the layer-changed signal is just a resonance frequency between the power layer and the ground layer, then the energy of such signal can be absorbed by the cavity resonators. The absorbed energy may form noises on the power layer/ground layer. Such noises may be transmitted through the whole power layer/ground layer to interfere with other signal lines that perform the signal layer change process, so that signal quality is decreased, and even a timing of the whole system goes failure, which may lead to abnormal operations of the system.
Presently, an electromagnetic bandgap (EBG) structure may be applied to resolve the aforementioned problems, in which a gandgap is designed to block the noises.